Process for chlorinating nitro aromatic hydrocarbons



Unite States atent 3,005,031 PROCESS FOR CHLORINATING NITRO AROMATIC HYDROCARBONS Martin E. Friedrich, Penns Grove, N.J., assignor to E. I. du Pont de Nemours and Company,,Wilmington, Del., a corporation of Delaware No Drawing. Filed Sept. 30, 1958, Ser. No. 764,246

9 Claims. (Cl. 260-646) nitroaromatic hydrocarbons by chlorinating nitroaromatic hydrocarbons. More particularly, the present invention is directed to overcoming the deleterious efiect of water in the chlorination of such representative nitro bodies as nitrobenzene and nitrotoluene by conducting the chlorination in the presence of a phosphorus chloride.

Nitoaromatic hydrocarbons may be directly chlorinated in the nucleus, at moderate temperatures, in the presence of a catalyst to produce the corresponding chloronitro bodies; this known process, in general, involves introducing chlorine gas into a mixture of the nitro body and catalyst, at a temperature at least suflicient to maintain the reaction mixture fluid and stirrable, untilthe desired degree of chlorination is achieved as is determined, for example,'by freezingpeint er spmific gravityea Readily produced in this way, for example, are monoand dichloronitrobenzene and nitrotoluenes," ofvalue as intermediates to, for example, the corresponding chloroaromatic amines for use in the manufacture of a variety of products, e.g., azo dyes, pigments and agricultural chemicals such as herbicides.

The chlorination of a nitro body such asnitrobenzene is known to be retarded, even inhibited completely by r the presence of extraneous substances, notably water and sulfuric acid. For example, Fierz-David and Blangey in 35 Fundamental Processes of Dye Chemistry (1949) state (p. 117) that the chlorination of nitrobenzene in the laboratory requires careful operation and succeeds only if the reaction is carried out in the complete absence officulty and high cost involved in getting down to waterlevels that can be tolerated. The chlorination of nitrobenzene, for example, even under optimum conditions, is a relatively slow reaction, and it has been found that to achieve practical rates of chlorination the water content of the system should be reduced to below 0.02% by weight of the nitrobenzene. Even at these trace quantity water levels, the rate of chlorination is apt to be unpredictable.

The nitroaromatic hydrocarbons, as ordinarily produced in nitration processes, contain water in proportions which, though small by ordinary standards, are suflicient to retard orinhibit the chlorination reaction. To reduce the water content to only 0.02% and below is time-consuming and costly, and,'not always successful because of the small proportions of water actually inaverage of 0.2%. Toppin wi'rlrcare ortopping fel lowed by distillation may provide distilled nitrobenzene 65 containing only 0.02% water, sometimes less. Similarly topped and distilled o-nitrotoluene will usually average 0.02% water, sometimes higher,e.g. 0.07%. Further, these low moisture grades of nitrobofdy readily absorb moisture from the air, so that unless they are carefully tents may increase several fold to prohibitively high levels.

'Further attempts to dry the nitro compounds by cofnf tacting them with solid desiccants such as calciumchloride or alumina gel have not been too successfuhand usualy result in some loss'of product.

Starting with dry apparatus and materials does not, however, avoid the possibility of contamination during storage and during the chlorination itself. Such contamination can be I particularly troublesome in humid weather: -During chlo- This invention is directed to the manufacture of chloro- '10 50 file removal of the C that is Produced 8 a product of the reaction is conveniently facilitated by maintaining a slight vacuum on the gas exit line leading from the reactor; if the reactor is not completely air-tight, moist air may be pulled into the reactor-and exert its retarding 15 effect. Also, when a ditferentnitro body, e.g. o-nitro toluene replaces another e.g. nitrobenzene, for'chlorination in a given reactor, the equipment usually has to be cleaned and washed, and as a result, despite attempts atcareful drying of the equipment the first charge chlorinated in it shows a retarded rate of chlorination.

impractical.

Sometimes the retarding effect of'watermay be overcome by the addition of extra quantities of catalyst to.

the reactor, but, besides adding to the costs, this too is not always satisfactory and the reaction often proceeds] I below the normal rate.

It is an object of the present invention to provide an I improved method of chlorinating nitroaromaticehydro carbons whereby the deleterious effects of water are obviated. Another object is to avoid the necessity of starting with scrupulously dried materials and apparatus, as has been suggested heretofore in the chlorination of the nitroaromatichydrocarbons.

These and other objects will be apparent inthe. specification and claims that follow. I I II I I More specifically, the present invention .is directed to the nuclear chlorination of a nitroaromatic hydrocarbon, Y which reaction is characterized as being retarded by trace quantities of water, the improvement of conducting the, chlorination in the presence of at least an approximate stoichiometric water-binding quantity of a phos phorus chloride. I I

According to the present novel process, introducing a phosphorus chloride, e.g. PO1 into the I chlorination mass in quantity about suflicient to react with any water the mononitrotoluenes, to produce the corresponding ringchlorinated aromatic compounds. Nitro bodies 'con-f' taining upto about 0.5% water by weight have been successfully chlorinated in the vpresence of approximate stoichiometrie',water-binding quantities of ,PCl The niti- 6 bodies ordinarily obtained by the'conventionalni tration and work-up procedures usually do not contain more than about 0.5% water, since the solubility 'of water in these substances is relatively low and gross amounts are readily separated therefrom by simple mechanical means. Reducing the' water content to about 0.5% is therefore no problem. For-example, p-nitroprotected immediately after distillationflheir water con--' toluene, recovered as the Washed solid product from the Patented oce z, 19 1 3 nitration reaction, usually contains 0.2 to 0.3% water. However," for chlorinationfits' water content heretofore had to be reduced to below 0.02%. As stated earlier, even at these-diflicultlyattainable low water levels, the reaction rate tends to" be unpredictable and slow, with J5- the result that production schedulesaredifiiculfto' main tain. TI'heseTdiflicul'ties-"are cleared up-by. the use of a phosphorus chloride according to the method ot-this in-. vention...

The present novel method involves adding-PC1 16 the nitro body'an'd catalystin quantity commensurate with the water content. of -the. system andconducting the chlorination in-the usual-:way. -Stoichionietrically, 2.54 partsby.

weight-.of..PCl are+requiredioreach part of water, based on the completeconversionof PO1 to P(OH) and I-ICl. Usually-a -25 to: 100%: excess -0ver the stoichiometric quantity will be 'ernployed' toensure complete-conversion e of thewater that m ayrbepresent toinnocuous products? Larger-quantities may .-be.-used, e.g. approximately three- (3) times the stoichiometric= quantity; however; such 95 chlorine and is--generallysatisfactory.

higher quantitiesare usually=considered unnecessary and wastefulr- Normally,::tlie quantity used will be basedon. the water contentiof the nitrocompound,'since the chlo rine gas and the chlorination-catalysts are easilymade reasonably dry for the present purpose. However; it should :be noted- -that .itis now *no longer necessary to rigorously adry all the materials :in order'to ensure the completerabsencefofxwater;:as has been recommended heretoforeri'of course,:-where ateasible the introduction of inhibiting amounts of water along with these materials shoulde'be avoided, to .minimizethe cost involved' in-the use of additionalquantities of P01 to tie-up such -quani tities ofiwater: 11,

It is p'referredyin thepre'sent novel processyto employ the equipment and the reaction conditions (temperature,- pressure' and catalyst) that have been established for-the known 'conventional process heretofore described.

A variety of-substances are known" catalystsfor the chlorination- -of nitrobenze'ne-and other-*aromatic nitro i compounds. Mosbcommonly'used are iron (powdered); salts of iron such as ferric chloride; iodine,'-'-"and their combinations. It is known, from other-workdn the litera-'=- 1 turefthat chlorine-convertsiron to ferric chloride; and

iodine to iodine chloride. The combinations of powdered iron 'and iodinefand of anhydrous ferric chloride and iodineare preferred. p

The actual quantities of catalyst may vary widelyfas describedinthe'art. "Relative to the" conventional process however; the use of PCl5.according..to' the method ofthe present invention "permits theme of smaller'quantities 'of" catalyst. In general, the quantity of iron.(or of ferric' chloride in" terms of 'itsiron .content) will rangefrorn about0.1% toabout 1.5% by weight ofthe nitro b'odyg'" usuallyiat leastabout' 0.3% will be preferredand not more thanabout 0.5% needed. I-he quantityof iodine will normally 'correspondto 0.02 to 0.1%, and usually not more 'than 0.03% by. weight of 'the'nitro b'ody': In general'also, the weightratio of'iron .to iodine'will be in the range 5:1 to 100:1;"and, usually'lOtl to 30:1.

Chlorination temperatures range from 1 about room temp'erature'sto 100C, usually from"'35 to 80 CL, and are preferably s'uchthat the reaction mass'is'moltenf and 'ea'silys stirredio facilitate contact'with chlorine. With"nitrobenzene and o'nitrotoluene,:40-50'Ciis the preferred. temperature range. With; pnitrotoluene; at least "6SZ' Cl is .needed .to keep the mass fluid!" To chlorina'te, chlorine is simplyl'passed "into the reac-j' tion mixtureo'f liquid nitro'bo'dy; catalYstand phos-i phorus trichloiid e. Preferably, the reaction mass is mechanically agitated'to aid-in the mixing of thereactants and iruthe expellingof theihydrogen chloride. formed in. the reaction. --The rate of. feed depends-:on the means available-for controlling-the desired-temperature .of-the reaction and on .the-capacity-of :the reaction medium to.

- as nit-robenzene and nitrotoluene with about one molart" at 40? C. To obtainmore'ofthe dichloro 'cornpound absorb and react with the chlorine being introduced. 'I'hus,"'the rate will vary depending on the temperature employed and on the particular nitro compound and catalyst, including proportions of catalyst. Preferably, the rate of feed will be such that the preferred temperatures are eastlymaintained and no free chlorine'appears in the hydrogen-'chloride exit gas streamlTo promote removal of hydrogen chlorideya slight uaouum' may be maintained,-if' desired; on the off-gas line 'Xitingfronfthe reactor. Elevated pressures are not n'e'cessaryior operabilityfTor reasons of' eco'nomyythe pressure will be atmospheric or slightly be'low'as indicated above.

It is also preferred,- where possible, to exclude-aipfrom the reaction mass, as-it has also been' found that airhas a retarding effect on the rate of chlorination." However, though air (oxygen)-free chlorine may be best -from:: this standpoint, for e'conomicreasons itis preferredte use chlorine vobtained directly from the electrolysis of NaCl brine. Such chlorine, after being scrubbed-with sulfuric acid and compressed, normally contains at' least As known;:catalyzedchlorination 015 nitro bodies'such equivalentofchlorine results in mixtures consistingprincipally 'of some -unreacted nitro compound and its monochloro 'and dichloro products. -Eitherthe monochloro ordichloro-products can be the major product depeuding'mainly on. the total amountof chlorine intro- I duced.-.-To obtain-predominantly monochloronitroben zene, for example,-::the reaction is continued 'untikthe product-attains a-specific: gravity of:about L3 to- 1.35 1.

the chlorination is :continued tohigher: specific gravi-z 35 ties; for example to 1.5 which will 'correspond'to-about" 35% monochloroand 65% dic'hlorobenzenem The freez: ing pointof the reaction-mass also indicates-the extent of chlorination. For the production of'monochloro p- .1 nitrotoluene,--for eXample,-chlorine is fed until the rise action producthas afreezingupoint of'52 -53 C.

It should be understood that the present im' ention is not'lirnitedto any particular' degreeof chlorination-for r:

- dioxide'and air; 55.

Exarfiple'l A charge -c onsistingof. 35,000 lbs. of nitrobenzene.

' containing-0.04% (14 lbs.) water, lbs. ofironfpow der, 1 0. lbs. of iodine and 38 lbs. of-phosphorus*trichloride, and contained in a-brick lined reactor"- was smoothly-monochlorinated as follows:

The above mixtur'e was agitated mechanically-and 4 a stream-of-chlorine gas passed into it-through a,feed

pipe-extending-belowthe surface of the charge, whereupon the absorption of chlorine with liberation of heat and hydrogen chloride started almostnimmediatelynv'l'he x the reactor, washed with aqueous hydrochloric acid to yield the monochlorinate product.

In contrast, in a series of otherwise identical runs in which PCl was omitted and in which nitrobenzene ter, based on said nitrobody, the amount of said water present being sufiicient to retard said nuclear chlorination, the improvement which comprises adding to said nitro aromatic hydrocarbon an amount of phosphorus having water contents ranging irom 6.fi65%' to 03%??? fi rhioririvsuficienntrmovercome the ehicminationretard was employed, the uptake of chlorine was slower and much less smooth: At least 60 hours and as long as 192 hours Were required to obtain a product of specific gravity 1.35 at 40 C., and during these runs the chlorine feed had to be carefully monitored, and slowed 10 down when free chlorine appeared in the oil-gas stream; furthermore, in some of the runs, additional catalytic quantities of iron powder and iodine had to be added for the reaction to proceed.

Further, in the recovery of the product, once the desired degree of chlorination has been attained, the charge is thoroughly washed with aqueous hydrochloric acid (as noted above) to remove the remaining catalyst. How many such washes are needed depends on how much iron was used as catalyst. Relative to the conventional process, the process of this invention required less iron, as should be apparent from the above comparisons, and, as a result, fewer washes were necessary in the work up of the chlorinated product.

Example 11 Similar improvements and economies were obtained as in Example I in the chlorination of p-nitrotoluene containing from 0.2% to 0.3% water by weight. In a typical run, a charge consisting of 4700 lbs. of wet p-nitro toluene (0.3% H 0), 60 lbs. iron, 1 lb. iodine and 20 lbs. 'PCI was smoothly chlorinated in a jacketed cast iron vessel at 60-65 C. to give a product of freezing point 53 C.

In contrast, the we p-nitrotoluene does not chlorinate under these conditions without PCl present; the reaction is impractically slow or inhibited altogether unless the moisture content is first reduced to less than 0.02%.

Example III 40 By the procedure of Example I, o-nitroluene (28,- 000 lbs. analyzing .QeQZZmruaIeQ, anhydrnumferrlzmhlmfi ride (350 lbs.), iodine (15 lbs.) and PCl (5'01bs., representing about 3 times the stoichiometric quantity) was smoothly converted at 40-50 C. to a monochlorinate of specific gravity 1.32 at 25 C.

When the phosphorus trichloride is omitted in the above procedure, the chlorination is erratic and usually about 30% slower.

As many apparently widely diflferent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. In the process of chlorinating a nitro aromatic hydrocarbon in the nucleus wherein chlorine is introduced into said nitro aromatic hydrocarbon in the presence of a nuclear chlorination catalyst, said nitro aromatic hydro- 60 carbon containing up to about 0.5% contaminating waing influence of said contaminating water.

2. The process of claim 1 wherein the phosphorus chloride is present in an amount from about 2.5 to 7.5 parts per part of said contaminating quantity of water.

3. In the process of chlorinating nitrobenzene in the nucleus wherein chlorine is introduced into said nitrobenzene in the presence of a nuclear chlorination catalyst, said nitrobenzene containing up to about 0.5 contaminating water, based on said nitrobody, the amount of said water present being suflicient to retard said nuclear chlorination, the improvement which comprises adding to said nitrobenzene an amount of phosphorus trichloride sutficient to overcome the chlorination retarding influence of said contaminating water.

4. In the process of chlorinating nitrotoluene in the nucleus wherein chlorine is introduced into said nitrotoluene in the presence of a nuclear chlorination catalyst, said nitrotoluene containing up to about 0.5% contaminating water, based on said nitrobody, the amount of said water present being suflicient to retard said nuclear chlorination, the improvement which comprises adding to said nitrotoluene an amount of phosphorus trichloride sufficient to overcome the chlorination retarding influence of said contaminating water.

5. In the process of chlorinating a nitro aromatic hydrocarbon in the nucleus wherein chlorine is introduced into said nitro aromatic hydrocarbon in the presence of a nuclear chlorination catalyst, said nitro aromatic hydrocarbon containing up to about 0.5% contaminating water by weight of said nitro aromatic hydrocarbon, the amount of said water present being suflicient to retard said nuclear chlorination, the improvement which comprises adding to said nitro aromatic hydrocarbon up to about 4% phosphorus chloride by weight of said nitro aromatic hydrocarbon, the amount of said phosphorus chloride being suflicient to overcome the chlorination retarding influence of said contaminating water.

6. The process of claim 5 wherein the phosphorus chloride is phosphorus trichloride present in an amount from about 2.5 to 7.5 parts per part of said contaminating amount of water.

7. The process of claim 5 wherein the nitro aromatic hydrocarbon is nitrobenzene.

8. The process of claim 5 wherein the nitro aromatic hydrocarbon is o-nitrotoluene.

9. The process of claim 5 wherein the nitro aromatic hydrocarbon is p-nitrotoluene.

References Cited in the file of this patent V Smith: College Chemistry, pp. 373-74 (1946), D.

Appleton-Century Co., Inc. (Copy in Scientific Library.)

Degering: An Outline of Organic Nitrogen Compounds, p. 138 (Sect. 430) (1950), University Lithopn'nters. (Copy in Scientific Library.) 

1. IN THE PROCESS OF CHLORINATING A NITRO AROMATIC HYDROCARBON IN THE NUCLEUS WHEREIN CHLORINE IS INTRODUCED INTO SAID NITRO AROMATIC HYDROCARBON IN THE PRESENCE OF A NUCLEAR CHLORINATION CATALYST, SAID NITRO AROMATIC HYDROCARBON CONTAINING UP TO ABOUT 0.5% CONTAMINATING WATER, BASED ON SAID NITROBODY, THE AMOUNT OF SAID WATER PRESENT BEING SUFFICIENT TO RETARD SAID NUCLEAR CHLORINATION, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID NITRO AROMATIC HYDROCARBON AN AMOUNT OF PHOSPHOROUS CHLORIDE SUFFICIENT TO OVERCOME THE CHLORINATION RETARDING INFLUENCE OF SAID CONTAMINATING WATER. 